diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index d8f3136..2047de5 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1528,6 +1528,7 @@ function template_preprocess_region(&$variables) {
   // Create the $content variable that templates expect.
   $variables['content'] = $variables['elements']['#children'];
   $variables['region'] = $variables['elements']['#region'];
+  $variables['attributes']['data-drupal-region'] = Html::getClass($variables['region']);
 }
 
 /**
diff --git a/core/modules/quickedit/js/quickedit.js b/core/modules/quickedit/js/quickedit.js
index 274913b..de8baa0 100644
--- a/core/modules/quickedit/js/quickedit.js
+++ b/core/modules/quickedit/js/quickedit.js
@@ -270,9 +270,10 @@
     var entityElement = $(fieldElement).closest(entityElementSelector);
     // In the case of a full entity view page, the entity title is rendered
     // outside of "the entity DOM node": it's rendered as the page title. So in
-    // this case, we must find the entity in the mandatory "content" region.
+    // this case, we find the main element of the page and use it as a full
+    // entity ancestor.
     if (entityElement.length === 0) {
-      entityElement = $('.region-content').find(entityElementSelector);
+      entityElement = $('[data-drupal-region="content"]').find(entityElementSelector);
     }
     var entityInstanceID = entityElement
       .get(0)
diff --git a/core/modules/system/templates/radios.html.twig b/core/modules/system/templates/radios.html.twig
index bf38830..e397644 100644
--- a/core/modules/system/templates/radios.html.twig
+++ b/core/modules/system/templates/radios.html.twig
@@ -12,4 +12,4 @@
  * @ingroup themeable
  */
 #}
-<div{{ attributes.addClass('form-radios') }}>{{ children }}</div>
+<div{{ attributes }}>{{ children }}</div>
diff --git a/core/modules/system/templates/region.html.twig b/core/modules/system/templates/region.html.twig
index b2c5471..e009455 100644
--- a/core/modules/system/templates/region.html.twig
+++ b/core/modules/system/templates/region.html.twig
@@ -14,14 +14,8 @@
  * @ingroup themeable
  */
 #}
-{%
-  set classes = [
-    'region',
-    'region-' ~ region|clean_class,
-  ]
-%}
 {% if content %}
-  <div{{ attributes.addClass(classes) }}>
+  <div{{ attributes }}>
     {{ content }}
   </div>
 {% endif %}